Given the way nostr relays work at the moment (text only) the data and traffic is relatively low. As NIP 95 is being implemented and enabled, which allows for storing of pics and video data on relays, the data/traffic will increase.
There's been a big debate on nostr between Damus and Amethyst developers about whether NIP 95 is a good idea. In the end it will depend on the relay runners to enable it or not.
Still early and most relay builds don't support the NIP yet. Will take a while I would expect.